1. Field of the Invention
The present invention relates to an opening and closing device for a window blind, in which respective louvers are suspended on a plurality of runners, for closing the window blind by widening distances between the louvers in a louver group and opening the window blind by stacking the louvers in the louver group.
2. Description of the Related Art
Conventionally, in the window blind of this type, a top or lead runner is pulled by a drive cord to sequentially draw the louvers from one by one from the louver attached to the top runner for folding the louver to open the window blind.
Therefore, when the window blind is opened up halfway, the louvers in the louver group are moved in a condition where they are stacked at the leading end of the opening to cause substantial load on a drive shaft for opening and closing the window blind, to damage the runner and/or drive shaft by wearing, or to degrade appearance.
On the other hand, in general, when a tilt shaft is pivoted by pulling a tilt cord, a carrier of all of runners extending through the tilt shaft are rotated simultaneously to vary angles of the louvers all together. When the louvers are placed in closed condition, the louvers are partially overlapped in back and forth direction constantly as viewed from the front side.
When the louver is in normal flat plate shape, partial overlap of the louvers in back and forth direction causes overlap of flat planes. This is the same even when the orientation of the louvers are turned over by reversing the front and back surfaces of the louvers by pivoting about 180.degree. all together by the tilt shaft. In either case, it is possible to open the window blind by sequentially pulling up the louver of the top runner. On the other hand, since partial overlap of the louvers in back and forth direction is overlap of the flat planes, to be substantially the same closed condition, therefore light blocking effect and continuity of color and/or pattern as viewed from the front side are not varied.
However, as disclosed in Japanese Examined Utility Model Publication No. Heisei 7-14623, in case of the window blind, in which the louver is curved in opposite direction in left and right halves to be formed into cross-sectionally reversed S-shaped configuration in order to provide wavy solid appearance, louvers are overlapped with fitting the curves with each other as shown in FIG. 1A. On the other hand, when the front and back surfaces of the louvers 4 are reversed by pivoting in the direction shown by arrow over about 180.degree. all together by the tilt shaft, curves are mated in back-to-back relationship as shown in FIG. 1B. In either case of FIGS. 1A and 1B, when the window blind is opened by pulling from the louver coupled with the top runner in these conditions, a difficulty is encountered. Also, gaps are formed between adjacent louvers to cause degradation of light blocking effect. Furthermore, the gaps are perceived as large step as viewed from the front side to potentially degrade continuity of color and/or pattern.
In the condition shown in FIG. 1B, it becomes possible to establish overlapping direction with fitting the curves similarly to FIG. 1A, by further pivoting the louvers 4 in the same direction to forcedly switch back and force positional relationship of portions mutually located in back to back relationship. However, by simultaneous pivot motion by the tilt shaft, it is not possible to reverse the louver all together to the position where the back and forth positional relationship of the portions of the louvers is switched. Therefore, it is not possible to reverse the louvers to the position same as FIG. 1A.